From cb120ed92d83568d790cee5849a093eda546b53f Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Thu, 26 Feb 2026 14:23:44 +0800
Subject: [PATCH 1/4] Fix LLVM-176877 for MSVC STL w/ Clang

---
 stl/inc/any                          |  9 +++++----
 tests/std/tests/P0220R1_any/test.cpp | 21 ++++++++++++++++++++-
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/stl/inc/any b/stl/inc/any
index c9d30736a57..9560c02911e 100644
--- a/stl/inc/any
+++ b/stl/inc/any
@@ -130,10 +130,11 @@ public:
         _Move_from(_That);
     }
 
-    template <class _ValueType, enable_if_t<conjunction_v<negation<is_same<decay_t<_ValueType>, any>>,
-                                                negation<_Is_specialization<decay_t<_ValueType>, in_place_type_t>>,
-                                                is_copy_constructible<decay_t<_ValueType>>>,
-                                    int> = 0>
+    template <class _ValueType,
+        enable_if_t<!is_same_v<decay_t<_ValueType>, any> && !_Is_specialization_v<decay_t<_ValueType>, in_place_type_t>,
+            int> = 0, // Separate these conditions into two `enable_if_t`s to avoid meta-recursion.
+                      // See LLVM-176877 and GH-6109.
+        enable_if_t<is_copy_constructible_v<decay_t<_ValueType>>, int> = 0>
     any(_ValueType&& _Value) { // initialize with _Value
         _Emplace<decay_t<_ValueType>>(_STD forward<_ValueType>(_Value));
     }
diff --git a/tests/std/tests/P0220R1_any/test.cpp b/tests/std/tests/P0220R1_any/test.cpp
index 391bb7b0ed1..2bf01073c69 100644
--- a/tests/std/tests/P0220R1_any/test.cpp
+++ b/tests/std/tests/P0220R1_any/test.cpp
@@ -1160,6 +1160,24 @@ void test_sfinae_constraints() {
     }
 }
 
+// https://llvm.org/PR176877
+// Avoid constraint meta-recursion for a type both convertible from and to std::any.
+template <class T, bool = std::is_copy_constructible<T>::value>
+void test_default_template_argument_is_copy_constructible(T) {}
+
+template <class T, bool = std::is_copy_constructible_v<T>>
+void test_default_template_argument_is_copy_constructible_v(T) {}
+
+void test_no_constraint_recursion() {
+  struct ConvertibleFromAndToAny {
+    ConvertibleFromAndToAny(std::any) {}
+  };
+
+  ConvertibleFromAndToAny src = std::any{};
+  test_default_template_argument_is_copy_constructible(src);
+  test_default_template_argument_is_copy_constructible_v(src);
+}
+
 int run_test() {
     test_copy_move_value<small>();
     test_copy_move_value<large>();
@@ -1167,8 +1185,9 @@ int run_test() {
     test_copy_value_throws<large_throws_on_copy>();
     test_move_value_throws();
     test_sfinae_constraints();
+    test_no_constraint_recursion();
 
-  return 0;
+    return 0;
 }
 } // namespace ctor::value
 // -- END: test/std/utilities/any/any.class/any.cons/value.pass.cpp

From a9ee19a09f9dc31501ab6f0089802d4d68d6c2a5 Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34@live.cn>
Date: Thu, 26 Feb 2026 17:25:18 +0800
Subject: [PATCH 2/4] Also mirror `#include <type_traits>`

... which is quite unnecessary, though.
---
 tests/std/tests/P0220R1_any/test.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tests/std/tests/P0220R1_any/test.cpp b/tests/std/tests/P0220R1_any/test.cpp
index 2bf01073c69..c8b1f4ec43c 100644
--- a/tests/std/tests/P0220R1_any/test.cpp
+++ b/tests/std/tests/P0220R1_any/test.cpp
@@ -1040,6 +1040,7 @@ int run_test()
 
 #include <any>
 #include <cassert>
+#include <type_traits>
 
 #include "any_helpers.h"
 #include "count_new.h"

From 9da89154262ecb2904e635475eceb7ba58520232 Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Thu, 26 Feb 2026 08:56:00 -0800
Subject: [PATCH 3/4] Cite the ordering guarantee.

---
 stl/inc/any | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/stl/inc/any b/stl/inc/any
index 9560c02911e..e9d7f0731dd 100644
--- a/stl/inc/any
+++ b/stl/inc/any
@@ -133,7 +133,9 @@ public:
     template <class _ValueType,
         enable_if_t<!is_same_v<decay_t<_ValueType>, any> && !_Is_specialization_v<decay_t<_ValueType>, in_place_type_t>,
             int> = 0, // Separate these conditions into two `enable_if_t`s to avoid meta-recursion.
-                      // See LLVM-176877 and GH-6109.
+                      // See LLVM-176877 and GH-6109. N5032 [temp.deduct.general]/7 guarantees:
+                      // "The substitution proceeds in lexical order and stops when
+                      // a condition that causes deduction to fail is encountered."
         enable_if_t<is_copy_constructible_v<decay_t<_ValueType>>, int> = 0>
     any(_ValueType&& _Value) { // initialize with _Value
         _Emplace<decay_t<_ValueType>>(_STD forward<_ValueType>(_Value));

From dac39bd17386e7e966b9a3f345f4785ff2dd71c4 Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Fri, 27 Feb 2026 12:43:14 -0800
Subject: [PATCH 4/4] any.cons/value.pass.cpp is now passing.

---
 tests/libcxx/expected_results.txt | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/tests/libcxx/expected_results.txt b/tests/libcxx/expected_results.txt
index f43ba600439..971a27c8889 100644
--- a/tests/libcxx/expected_results.txt
+++ b/tests/libcxx/expected_results.txt
@@ -1112,9 +1112,6 @@ std/input.output/file.streams/fstreams/filebuf.virtuals/xsputn.pass.cpp:1 FAIL
 std/utilities/meta/meta.unary/meta.unary.prop/is_implicit_lifetime.pass.cpp:0 FAIL
 std/utilities/meta/meta.unary/meta.unary.prop/is_implicit_lifetime.pass.cpp:1 FAIL
 
-# Not analyzed. Clang error: no member named 'value' in 'std::is_copy_constructible<ConvertibleFromAndToAny>'
-std/utilities/any/any.class/any.cons/value.pass.cpp:2 FAIL
-
 # Not analyzed. Assertion failed: globalMemCounter.checkOutstandingNewLessThanOrEqual(1)
 std/input.output/filesystems/class.path/path.member/path.assign/move.pass.cpp FAIL
 std/input.output/filesystems/class.path/path.member/path.construct/move.pass.cpp FAIL